Applied Radiology

Dr. Raskin is on the voluntary faculty at Jackson Memorial Hospital and is a Clinical Associate Professor of Radiology at the University of Miami School of Medicine. He is a practicing diagnostic radiologist at University Medical Center in Tamarac, FL. He is also a member of the editorial board of this journal.

The abnormal interpretation of an MRI scan of the spine is often the reason why a personal injury attorney will pursue a claim against the defendant in a motor vehicle accident or a slip and fall injury. The wording of the report can have significant legal implications. Confusing, ambiguous terminology in describing the disc can lead to significant unwarranted settlements or jury verdicts. The interpreting radiologist should be cognizant of the implications of an "abnormal" finding.

Inconsistencies between subjective complaints and objective diagnostic tests

Asymptomatic individuals with "abnormal" MRI--Recent literature has shown that many anatomical abnormalities of the back, including disc bulges and disc herniations, are quite common in people without back pain. ¹ Even prior to magnetic resonance imaging (MRI), the high incidence of disc abnormalities in the lumbar spine of asymptomatic individuals was quite well known. In 1956, a study using postmortem examinations of the entire spine showed a 39% prevalence of posterior disc protrusions. ² In 1968, a study using myelography in 300 asymptomatic individuals demonstrated lumbar disc abnormalities in 24%. ³ Using computed tomography (CT), a 1984 study reported the prevalence of herniated discs in asymptomatic individuals to be 20% in those under the age of 40 years and 27% in those over the age of 40. ⁴ Since MRI became a clinically available diagnostic imaging tool in the mid 1980s, multiple studies have confirmed that more than half of adults without symptoms have significant disc bulges or disc herniations. ⁵ Furthermore, the prevalence of disc herniations increases with age.

Symptomatic individuals with "normal" MRI--This is a difficult category to properly assess, since back pain is so common, affecting nearly half of all adults during a given year. Furthermore, over two-thirds of adults have back pain at some time in their lives. ⁶ Back pain is the leading cause of work-related disability and the second leading reason for physician visits in the United States.

Symptomatic individuals with "abnormal" MRI--By far, this group is the most difficult of all to evaluate and assess properly. The high prevalence of anatomical abnormalities in individuals without symptoms, combined with the high prevalence of back symptoms in adults, makes the likelihood of coincidental findings quite high. Since more than half of asymptomatic individuals have disc abnormalities consisting of either significant disc bulges or disc herniations, it is not unreasonable to assume that more than half of the individuals involved in motor vehicle accidents or slip and falls will also have abnormal discs unrelated to their "accident." The real question that needs to be answered is, can we attribute the findings seen on an MRI scan to a particular accident or event? The question is not merely rhetorical, as it has grave financial implications in our litigious society. With further improvements in resolution of MRI scans, more and smaller abnormalities are detected, even though these findings may not be clinically relevant.

Myths about neck and low back pain ⁷

If you have a disc herniation, you must have surgery--Most disc herniations get better on their own. Surgery would rarely be indicated for a disc bulge. Surgery rates for back pain in the United States are five times more common than in England and more than twice that in Scandinavia. Surgery for patients whose back pain is associated only with an abnormal imaging study without objective clinical findings may be unnecessary, as well as detrimental to the patient. Some patients with back pain become worse after surgery. Complicating this situation even more is the fact that most patients with acute low back pain get better regardless of differing treatments.

MRI scans can always identify the cause of pain--Most MRI scans in patients with pain reveal a normal MRI scan or abnormalities on the MRI scan that are not correlated to the pain.

If your back hurts, you should take it easy until the pain goes away--Studies have shown that those who remain active despite acute pain, experience less pain lasting >=3 months.

Most back pain is caused by injuries or heavy lifting--This is not true. Most back pain occurs without any evidence of related injury. Up to 85% of patients with low back pain are left without a definitive diagnosis for their pain. Most patients cannot recall any specific incident that caused their pain. Injuries or heavy lifting, although risk factors, do not account for most episodes. Back pain can be caused by being overweight or by stress. Physical activity resulting in muscle soreness can result in some back pain, as does the natural wear and tear that occurs with age. Simply put, we do not know the cause of most back pain.

Back pain is usually disabling--Studies have shown that it is often more useful to have patients with back pain return to some form of light work as quickly as possible. Those that do so experience less long-term pain than those who rested and waited for the pain to diminish. In most individuals, the pain will get better on its own.

Everyone with back pain should have x-rays of the spine--X-rays are negative in most individuals with back pain. Other than ruling out rare congenital abnormalities, infections, fractures, rare forms of arthritis, or neoplasms, the spine x-ray has little or no effect on treatment.

Bedrest is the mainstay of therapy--This was the standard therapy until about 10 years ago. This has never been shown to be effective. Resuming normal activities as much as possible may be the best option for patients with acute back pain.

Loss of the normal lordotic curve is indicative of muscle spasm in the neck--It is not unusual to see a radiology report that states, "loss of the normal lordotic curve, compatible with muscle spasm," in a patient involved in a motor vehicle accident. The curvature of the neck vertebrae is usually assumed to be lordotic. Lordosis refers to the anterior concavity and the curvature of the cervical spine as viewed from the side. When there is "loss" of the normal lordotic curve of the cervical spine, this is often referred to as "straightening" of the normal lordotic curve. It has been suggested that spasm of the muscles are the cause of loss of the normal lordotic curve. In a recent study, the cervical curvature of 488 patients with "acute whiplash injury" were compared to the cervical curve in 495 healthy asymptomatic controls. It was reported that there was no significant differences in the neck curvature between the groups and there was no significant association between clinical symptoms and the curvature of the neck. ⁸ This study raises serious questions about the importance of the "normal lordotic curve" as a marker of clinical importance.

Disc anatomy

Basically, the intervertebral disc is comprised of two parts: the outer part and the inner part. The outer part is called the annulus fibrosus and is composed of up to 90 layers of laminated, interdigitating collagen fibers that are at approximately a 30š bias. The annulus fibrosus is thick and fibrous and its purpose is to contain the inner portion of the disc. This inner portion is gelatinous and is called the nucleus pulposus. The purpose of this portion of the disc is to act as a shock absorber. This is the portion of the disc that herniates when there is a tear or rent in the annulus. With increasing age, the integrity of the annulus is compromised and the gelatinous nucleus pulposus starts to lose water and desiccate. Initially, the nucleus pulposus is comprised of approximately 80% water, but a desiccated disc may contain ¾60% water. Therefore, with increasing age, there is less disc to herniate and traumatic disc herniations are less frequent.

Disc abnormalities

The term "herniation" is a catchall term that has been used to describe a wide spectrum of disc abnormalities extending beyond the interspace. We need to strive to use morphological terms that can be more defined precisely to avoid confusion. The American Spine Society has suggested the following morphological terms when describing the disc: ⁹

Normal disc--The margins of the disc do not extend beyond the interspace.

Disc bulge--A circumferential symmetrical extension of the disc that extends beyond the interspace.

Disc protrusion--Focal or asymmetrical extension of the disc beyond the interspace with the base against the disc of origin being broader than any other dimension.

Extruded disc--A more pronounced extension of the disc beyond the interspace with the base against the disc of origin being narrower than the diameter of the extruding material itself.

Sequestered disc--The extruded disc no longer has a connection between the disc material and the disc of origin. This is also called a free disc fragment.

Significance of MRI findings

Dating the time of a disc herniation--An MRI scan, by itself, cannot date the time of occurrence of disc bulge or disc herniation. The MRI scan merely shows that a disc herniation is present at the time of the MRI scan.

Most lumbar disc herniations are degenerative--Disc herniations occur with increasing frequency with age and are frequently present in asymptomatic individuals. Disc bulges are part of a degenerative process and not related to a single traumatic event. ¹⁰

Significance of bony changes--Bony changes often take the form of spondylosis or facet arthropathy. The bony changes seen on an MRI scan take years to develop and are often in response to, and as a consequence of, disc degeneration and even disc herniation. Since the bony changes take years to develop, if they are seen in association with a disc abnormality at the same level, it is more likely that all of the findings seen are degenerative in nature and not related to recent trauma. This does not mean that a disc herniation cannot occur from trauma, but merely that when a disc herniation is accompanied by bony degenerative changes at the same level, the disc herniation is more likely to be a degenerative disc herniation rather than one related to a recent acute traumatic event.

Understanding annular tears ^11,12 --On MRI scans, annular tears are usually evident by a high signal intensity zone within the posterior fibrous ring of the intravertebral disc. Previously, these findings were considered to be predictive of discogenic pain. However, more recent studies have shown that these high intensity zones are frequently found in asymptomatic volunteers.

Conclusions

MRI is still the best diagnostic test for determining disc abnormalities. However, due to the high prevalence of asymptomatic individuals with abnormalities, combined with the high prevalence of symptoms, caution should be used in trying to relate a specific abnormality to a symptom. The inconsistencies between subjective complaints and the MRI findings must be recognized, as well as the legal implications of relating an abnormal finding with a particular accident or event. AR